1、Designation: A 956 06Standard Test Method forLeeb Hardness Testing of Steel Products1This standard is issued under the fixed designation A 956; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in
2、parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the determination of the Leebhardness of steel, cast steel, and cast iron (Part A), includingthe methods for the verifi
3、cation of Leeb hardness testinginstruments (Part B), and the calibration of standardized testblocks (Part C).NOTE 1The original title of this standard was “Standard Test Methodfor Equotip Hardness Testing of Steel Products.”11.2 The values stated in inch-pound units are to be regardedas standard. Th
4、e values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard t
5、o establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 Definitions:3.1.1
6、 calibrationdetermination of the values of the sig-nificant operating parameters of the instrument by comparisonwith values indicated by a reference instrument or by a set ofreference standards.3.1.2 Leeb hardness numbera number equal to the ratio ofthe rebound velocity to the impact velocity of a 3
7、-mm or 5-mm(based on the type of impact device) diameter tungsten carbideball or diamond tipped impact body, multiplied by 1000.L 5Rebound VelocityImpact Velocity3 1000The Leeb hardness number is followed by the symbol HLwith one or more suffix characters representing the type ofimpact device.3.1.3
8、Leeb hardness testa dynamic hardness test methodusing a calibrated instrument that impacts a spherically shapedcarbide ball or diamond tipped body with a fixed velocity(generated by a spring force) onto a surface of the materialunder test. The ratio of the rebound velocity to the impactvelocity of t
9、he impact body is a measure of the hardness of thematerial under test.3.1.4 surface finishall references to surface finish in thistest method are defined as surface roughness (that is, Ra =average roughness value, AA = arithmetic average).3.1.5 verificationchecking or testing the instrument toensure
10、 conformance with this test method.4. Significance and Use4.1 Hardness of a material is a poorly defined term that mayhave many meanings depending on the type of test performedand the expectations of the person involved. The Leeb hardnesstest is of the dynamic or rebound type, which primarilydepends
11、 both on the plastic and on the elastic properties of thematerial being tested. The results obtained are indicative of thestrength and dependent on the heat treatment of the materialtested.4.2 The Leeb hardness test is a superficial determinationonly measuring the condition of the surface contacted.
12、 Theresults generated at that location do not represent the part atany other surface location and yield no information about thematerial at subsurface locations.A. GENERAL DESCRIPTION OF INSTRUMENTSAND TEST PROCEDURE FOR LEEB HARDNESSTEST5. Apparatus5.1 The instrument used for Leeb hardness testing
13、consistsof (1) an impact device that is equipped with a tungsten carbideball or synthetic diamond tipped impact body, an induction coil1This test method is under the jurisdiction of ASTM Committee A01 on Steel,Stainless Steel and Related Alloys and is the direct responsibility of SubcommitteeA01.06
14、on Steel Forgings and Billets.Current edition approved Sept. 1, 2006. Published September 2006. Originallyapproved in 1996. Last previous edition approved in 2002 as A 956 02.Leeb and Equotip are registered trademarks used with permission of Proceq SA.2For referenced ASTM standards, visit the ASTM w
15、ebsite, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Har
16、bor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.velocity measuring assembly, and a support ring, and (2)anelectronic digital display hardness indicating device.5.2 Impact DevicesThere are six types of impact devicesused in Leeb hardness testing. These are the D, DC, D+15, G,C
17、, and the E impact units. Brief descriptions of the types ofdevices and their common applications are given in AppendixX1.5.3 Summary of Test MethodDuring a hardness test, animpact body with a spherically shaped tungsten carbide ordiamond tip impacts under spring force, the test surface fromwhich it
18、 rebounds. The impact and rebound velocities aremeasured when the impact body is approximately 1 mm fromthe test surface. This is accomplished by means of a permanentmagnet mounted in the impact body which, during the test,moves through a coil in the impact device and induces anelectric voltage on b
19、oth the impact and rebound movements.These induced voltages are proportional to the respectiveimpact and rebound velocities. The quotient of these measuredvoltage values derived from the impact and rebound velocities,multiplied by the factor 1000 produces a number whichconstitutes the Leeb hardness
20、value.5.4 See 7.1.1 when using replacement machine components.6. Test Piece6.1 FormThe Leeb hardness test is acceptable for steel,cast steel, and cast iron with varying shapes and sizes.6.2 Thickness and WeightThe thickness and weight of thetest piece shall be considered when selecting the impact de
21、viceto be employed. The following guidelines are offered asminimum weights and sizes of test pieces for selecting theproper test equipment. Test pieces of weights less than theminimum or pieces of any weight with sections less than theminimum thickness require rigid support and coupling to athick, h
22、eavier non-yielding surface to resist the impact of thedevice. Failure to provide adequate support and coupling willproduce test results lower than the true hardness value.Impact Device Weight (min) or Thickness (min)D, DC, D+15, E 15 lb (5 kg)18 in. (3 mm)G 40 lb (15 kg)38 in. (10 mm)C 4lb(1.5kg)13
23、2 in. (1 mm)6.3 CurvatureTest pieces with curved surfaces may betested on either the convex or concave surfaces providing thatthis radius of curvature of the specimens is matched to the sizeof the support ring and is not less than 2 in. (50 mm) for the Gimpact device or 1316 in. (30 mm) for other im
24、pact devices.6.4 Surface Finish/PreparationThe test surface shall becarefully prepared to avoid any alterations in hardness causedby heating during grinding or by work hardening duringmachining. Any paint, scale, pits, or other surface coatingsshall be completely removed. The surfaces to be tested s
25、hall besmooth. Failure to provide adequate surface finish will producequestionable test results. Coarse finishes will tend to lower themeasured value. It is recommended that the test surface bemachined or ground and polished to the following finishes.(The grinding wheel grit size shown for each fini
26、sh is offeredfor guidance in achieving the finish noted.)Impact Device Surface FinishRa(max)Grit Size (Approx.)D, DC, D+15, E 63 in. (2 m) 200G 250 in. (7 m) 65C 16 in. (0.4 m) 5006.5 Magnetic FieldsPerformance of the Leeb hardnesstest on parts with a residual magnetic field may affect theresults. I
27、t is recommended that any residual magnetic field beless than 4 G.6.6 VibrationVibration of the test specimen may affect theresults of the Leeb hardness test. It is recommended that thistest be performed with the test piece at rest.6.7 TemperatureThe temperature of the test piece mayaffect the resul
28、ts of the test. In addition, this effect may bedifferent for different materials. Testing to this procedure shallbe performed with the temperature of the test piece between40F (4C) and 100F (38C). At temperatures outside thisrange, the user shall develop a temperature correction for thespecific mate
29、rial being tested.7. Verification of Apparatus7.1 Verification MethodPrior to each shift, work period,or use, and following a period of extended continuous use(1000 impacts), the instrument shall be verified as specified inPart B. Any instrument not meeting the requirements of Part Bshall not be emp
30、loyed for the acceptance testing of product.7.1.1 Cautionary note: When replacement parts are used ina Leeb hardness tester it is important that they be fullycompatible with the original equipment, otherwise incorrecthardness readings may be obtained. Calibration using a singlestandard test block ma
31、y indicate acceptable results, but addi-tional calibration tests using blocks of differing hardness mayyield unacceptable results. If replacement, non-original equip-ment parts are used, multiple block calibration verification isstrongly advised. Specifically, one calibration block of ahardness equa
32、l to or lower than the minimum expectedhardness of the material being tested, one calibration block ofa hardness equal to or greater than the maximum expectedhardness of the material being tested, and one calibration blocknear the middle of the range should be used.8. Procedure8.1 Test MethodTo perf
33、orm a hardness test, the impactdevice is connected to the indicator device and the instrumentis turned on. The impact device, while not in contact with thetest piece, is held firmly with one hand and the charging tubeis depressed with the other hand until contact is felt. Thecharging tube is allowed
34、 to slowly return to the startingposition. The impact body is now in its loaded or lockedposition. After placing the impact device on the test surface,trigger the impact body by exerting a light pressure on therelease button. The Leeb hardness value is read on the indicatordevice.8.2 AlignmentTo pre
35、vent errors resulting from misalign-ment, the base support ring of the impact device shall be heldsnugly and perpendicular to the surface of the test piece.8.3 Impact DirectionThe impact device is calibrated forthe down vertical impact direction (perpendicular to a horizon-tal surface). For other im
36、pact directions such as 45 from thehorizontal plane or from underneath, the measured hardnessA956062values will require adjustment (see 9.2). Some newer modelsautomatically compensate for test direction.8.4 Spacing IndentationsThe distance between any twoimpact points shall not be less than two diam
37、eters edge-to-edge. The distance between the impact point and a specimenedge shall not be less than three diameters edge-to-edge. Nopoint shall be impacted more than once.8.5 Reading the Leeb Instrument Hardness values in Leebunits are read directly on the electronic display of the indicatordevice.
38、The indicated value is automatically replaced with thenext test impact result.8.6 Number of ImpactsFive impacts in an area of approxi-mately 1 in.2(645 mm2) shall constitute a test. If the materialbeing tested is considered to be nonhomogeneous (for ex-ample, cast iron) ten impacts in an area shall
39、be made toconstitute a test.9. Calculation of Hardness Result9.1 The hardness test result shall be the arithmetic averageof the five individual impact readings in the measuring area.9.2 Correction for Test DirectionWhen using an Leebinstrument without automatic compensation for test direction,the co
40、rrection value for direction of test impact is to besubtracted from the average value determined for the measur-ing area. This correction value can be determined in accor-dance with Tables 1-6.10. Conversion to Other Hardness Scales or TensileStrength Values10.1 There is no direct correlation betwee
41、n the Leeb hard-ness test principle and other hardness methods or a tensilestrength test. All such conversions are, at best, approximationsand therefore conversions should be avoided except for specialcases where a reliable basis for the approximate conversion andthe accuracy of the conversion has b
42、een obtained by compari-son testing. No conversions shall be employed without specificagreement between the party specifying this test method andthe party performing the hardness test.11. Report11.1 Report the following information:TABLE 1 Correction Values for Other Impact Directions:Device DLD300-
43、6 -12 -20 -29350-6 -12 -19 -27400-5 -11 -18 -25450-5 -10 -17 -24500-5 -10 -16 -22550-4 -9 -15 -20600-4 -8 -14 -19650-4 -8 -13 -18700-3 -7 -12 -17750-3 -6 -11 -16800-3 -6 -10 -15850-2 -5 -9 -14900TABLE 2 Correction Values for Other Impact Directions:DeviceD+15LD+15300-7 -14 -26 -38350-7 -13 -25 -3640
44、0-6 -12 -23 -34450-6 -12 -22 -32500-6 -11 -21 -30550-6 -11 -20 -28600-5 -10 -19 -27650-5 -10 -18 -25700-5 -9 -17 -24750-4 -9 -16 -22800-4 -8 -15 -21850-4 -8 -14 -20900TABLE 3 Correction Values for Other Impact Directions:Device ELE300-5 -9 -18 -26350-4 -9 -17 -24400-4 -9 -16 -22450-4 -8 -15 -21500-4
45、 -8 -14 -20550-4 -8 -13 -18600-3 -7 -12 -17650-3 -7 -12 -16700-3 -6 -11 -15750-3 -6 -10 -14800-3 -5 -9 -13850-2 -5 -8 -12900A95606311.1.1 The average Leeb hardness number for each test areawith the impact device indicated (for example, xxx HLD or xxxHLD+15).11.1.2 When hardness values converted from
46、 the Leebnumber are reported, the instrument used shall be reported inparentheses, for example, HB (HLG).12. Precision and Bias12.1 Precision:12.1.1 Interlaboratory Test ProgramAn interlaboratorytest program was conducted in accordance with to developinformation regarding the precision of the Leeb h
47、ardnessmeasurements. Eight laboratories tested five certified testblocks. Each laboratory measured the hardness of each block25 times.12.1.2 Test ResultThe precision information given belowis the average of the five certified test blocks, each of a differenthardness.12.1.3 Repeatability and Reproduc
48、ibility:95 % Repeatability Limit (within laboratory) = 4.4 %95 % Reproducibility Limit (between laboratories) = 8.8 %12.1.3.1 The terms in 12.1.3 (repeatability limit and repro-ducibility limit) are used as specified in Practice E 691. Therespective standard deviations among test results, related to
49、 theabove numbers by the factor 2.8, are:Repeatability Standard Deviation = 1.6 %Reproducibility Standard Deviation = 3.2 %12.2 BiasSince hardness is not an intrinsic property of amaterial, there is no basis on which to determine or assign anaccepted reference value. Consequently, there is no basis fordefining the bias of this test method.B. VERIFICATION OF LEEB HARDNESSINSTRUMENTS13. Scope13.1 Part B covers the procedure for verification of Leebhardness instruments by a standardized block method.14. General Requirements14.1 Before a Leeb har
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